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XV. — Some Miscellaneous Observations on the Salmonidoe. By John Davy, M.D., 

 F.R.S. Lond. &Edin., Inspector-General of Army Hospitals. 



(Read 18th December 1854.) 



The interests connected with the natural family of the Salmonidae, both in rela- 

 tion to river-sport, the pleasant recreation of angling, and to material wealth, in the 

 instances of the migratory kinds, are so considerable and fully admitted, that I 

 trust no apology is required for submitting to the Society any observations in the 

 least likely to contribute to a more intimate knowledge of the species, whether as 

 regards their structure or their habits. 



1. Of the Air-Bladder of the Salmonidce and its contained Air 

 I have examined this organ and the air contained in it in the salmon, white 

 trout (S. trutta), charr, and common trout. In each instance I have found it 

 very similar ; of a cylindrical form, tapering at each extremity, composed of a 

 transparent membrane, very faintly and partially vascular, extending the whole 

 length of the abdomen, and, with one exception, without colour. The exception 

 was that of the charr, in which, when the fish were strongly coloured red (their 

 muscular substance), it, the air-bladder, was often seen of a rose-hue. I have not 

 been able to detect in any of these fish a communication between the air-bladder 

 and the oesophagus. 



The proportional size of the organ, or the quantity of air distending it, on 

 which its size, no doubt, very much depends, varies, it would appear, in different 

 fish of the same species, and still more in those of different species. Commonly, 

 I believe, the bladder of the migratory kinds, as the salmon and white trout, is 

 smaller or less distended than that of the common trout and charr. In a fresh-run 

 salmon of about 12 lbs. taken with the net in the first week of August at Bally- 

 shannon, opened half an hour after its capture, I found in its bladder only about 

 a quarter of a cubic inch of air. And one of the men, an intelligent person be- 

 longing to the fishing establishment of that place, who, this last season, had, he 

 said, opened about two hundred fresh-run fish, varying in weight from about 8 to 

 28 lbs., assured me that, as well as he could remember, the quantity of air was 

 " oftener under than over half a wine-glassful." 



For the purpose of chemical examination, of course, it was necessary to open 

 the fish under water. The contained air. extricated on puncturing the blad- 

 der, was collected in a graduated tube. For carbonic acid, it was tested by agi- 



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